(1) Field of the Invention
The present invention relates to a process for producing erythritol as a kind of polyols by using erythritol-producing microorganisms.
Erythritol is also called erythrit, and has the following characteristics:
______________________________________ Melting point: 122.degree. C., Decomposed temperature: 329.degree. C., Chemical formula: CH.sub.4 O.sub.4 H.sub.10, Rational formula: CH.sub.2 OHCHOHCHOHCH.sub.2 OH, Chemical structure: ##STR1## ______________________________________
Erythritol is a kind of sugaralcohols, and demand for erythritol has recently been increasing due to its sweetness twice that of sucrose.
(2) Related Art Statement
Processes have already been known for producing erythritol by using erythritol-producing microorganisms. For example, Japanese Patent Application Laid-open Nos. 60-110,295 and 61-31,091 disclose processes for producing erythritol from fermentable saccharides such as glucose with use of the erythritol-producing microorganisms, and U.S. Patent No. 3,756,917 discloses a process for producing erythritol from hydrocarbons. However, as described in these publications, there have heretofore been employed batch type producing processes in which a substrate and erythritol-producing microorganisms are charged into a fermentation tank and fermented for 1 to 2 weeks, a broth is taken out from the tank, and a reaction product is separated therefrom. Therefore, the conventional processes have problems in that the volume of the producing apparatus is great, that the production cost is high, and that the production rate of the erythritol cannot be increased to not less than 1.5 g/l.H. In order to solve the above problems, the present inventors have tried a continuous fermentation process in which a liquid inside a tank is extracted, while a substrate is continuously charged thereinto. However, since it was difficult to maintain the concentration of cells at a high level due to much flowout of the cells, the erythritol production rate could not greatly be increased.